Microbiocidal compositions

The present invention relates to microbiocidal compositions, in particular microbiocidal compositions for use in cosmetic formulations.

It is desirable for cosmetic formulations to have a long shelf life. However, cosmetic formulations tend to degrade over time owing to bacterial or fungal growth in the formulation. There is therefore a desire to produce formulations that have an improved resistance to microbial attack, both from bacteria and fungi.

While chlorinated isothiazolones have been used in cosmetic formulations and are effective in relatively small concentrations, they have been found to be unstable with variations in pH and/or temperature. The chlorinated isothiazolones may also trigger allergies and this further restricts their use. Moreover, they may be incompatible with some cosmetic raw materials, especially raw materials which act as nucleophiles or reducing agents.

It is an object of the present invention to overcome, or at least mitigate, some of the problems associated with the compositions of the prior art.

Accordingly, the present invention provides a microbiocidal composition comprising:

a non-halogenated 2-alkyl-3-isothiazolone, and

chlorphenesin and/or an alkane diol,

wherein the alkyl group in the non-halogenated 2-alkyl-3-isothiazolone comprises 1 to 4 carbon atoms,

the alkane diol comprises 5 to 12 carbon atoms, and

the hydroxyl groups of the alkane diol are vicinally substituted.

Non-halogenated 2-alkyl-3-isothiazolones may act as biocidal agents. However, when used alone their performance in preventing growth of bacteria and fungi is relatively poor in comparison with an equivalent concentration of chlorinated isothiazolones.

However, non-halogenated 2-alkyl-3-isothiazolones have unexpectedly been found to be relatively stable to variations in pH and/or temperature compared to chlorinated isothiazolones. Furthermore, non-halogenated 2-alkyl-3-isothiazolones have been found to be more compatible than chlorinated isothiazolones with the raw materials typically present in cosmetic formulations.

It has also surprisingly been found that the combination of the non-halogenated 2-alkyl-3-isothiazolone and the alkane diol results in a synergistic effect in preventing microbial growth. As a consequence, a lower concentration of the non-halogenated isothiazolone may be used to effectively prevent microbial growth.

It has also been surprisingly found that the combination of a non-halogenated 2-alkyl-3-isothiazolone and chlorphenesin has a synergistic effect in preventing microbial growth.

The combination of the 2-alkyl-3-isothiazolone, chlorphenesin and the alkane diol results in a particularly effective microbiocidal composition in which all the ingredients have been found to act synergistically, i.e. the biocidal effect is greater than would be expected purely on the efficacy of the components alone.

Preferably, the 2-alkyl-3-isothiazolone and the alkane diol are present in the composition in a ratio (wt. %) range of from 1:3 to 1:400, more preferably of from 1:10 to 1:50, still more preferably of from 1:15 to 1 to 30. The 2-alkyl-3-isothiazolone and the alkane diol may be present in the composition in a ratio (wt. %) range of from 1:25 to 1:48, still more preferably from 1:30 to 1:45.

Preferably, the 2-alkyl-3-isothiazolone and the chlorphenesin are present in the composition in a ratio (wt. %) range of from 10:3 to 1:400, more preferably of from 1:10 to 1:50, still more preferably from 1:15 to 1:45, more preferably 1:15 to 1:30.

The ratio of 2-alkyl-3-isothiazolone:alkane diol:chlorphenesin may be in the range of from 1:10:10 to 1:20:20 (i.e. varying independently the amounts of alkane diol and/or chlorphenesin between their preferred upper and lower limits relative to the amount of isothiazolone).

The alkyl group in the 2-alkyl-3-isothiazolone may be substituted or non-substituted and may be branched or linear. The alkyl group may be substituted with one or more of the following: hydroxyl, cyano, alkylamino, carboxy, carboalkoxy and alkylthio.

Preferably, the non-halogenated 2-alkyl-3-isothiazolone is 2-methyl-3-isothiazolone.

It has been found by the inventors that different alkane diols exhibit different biocidal efficacies in combination with 2-alkyl-3-isothiazolones.

The alkane diol may comprise 5 to 12 carbon atoms. The alkane diol may comprises 5 to 10 carbon atoms, more preferably 6-8 carbon atoms, which may be in a linear or branched chain, preferably a linear chain. Preferably the alkane diol comprises 6 or more carbons. The alkane diol may be selected from one or more of 1,2-pentanediol, 1,2-hexanediol and 1,2-octanediol. The alkane diol may be 1,2-octanediol. It has been found that the antimicrobial activity of C5 alkane diols is surprisingly poor, the reasons for which are not fully understood (see Table 1A of the examples). Preferably, therefore, the alkane diol comprises at least 6 carbons.

The alkane diol may comprises 9 to 12 carbons, preferably 10, 11 or 12 carbons, most preferably 10 carbons. The alkane diol may be selected from 1,2-decanediol and 1,2-dodecanediol. It has been surprisingly found that alkane diols comprising 9 to 12 carbons offer greater biocidal efficacy than lower alkane diols.